Rubber thread and method for making the same



Nov. 24, 1936.

C. L. BEAL RUBBER THREAD AND METHOD FOR MAKING THE SAME Filed Oct. 11, 1933 w Ivy-"E nib 1555/ .L 1325/ Patented Nov; 24, 1936 p v 2,061,749

UNITED STATES PATENT OFFICE V RUBBER THREAD AND METHOD FOR MAKING THE SAME can L. Beal, Cuyahoga Falls, ohm, assignor to American Anode, Inc., Akron, Ohio, a corporation of Delaware Application october 11,1933, Serial No. 693,113

9 Claims. (01.18-54) This invention relates to elastic rubber thread thread; the provision of rapid and economical such as that used for making stretchable fabmeans for producing from liquid latex large quanrics for garments, etc. and relates especially to titles of rounded thread; andother objects which a novel method and apparatus for making from will be apparent from the following description liquid rubber latex a substantially round rubber of the invention. thread which will be admirably suited for weav- My invention, in a preferred embodiment, coming with textile threads to make elastic fabrics, prises forming from liquid rubber latex a conand for other uses. i tinuous coherent sheet of rubber coagulum, and Heretofore such rubber thread has been made drying the sheet, if at all,to the extent only 10 commercially in one of two manners; In the that the coagulum retains sufilcient surface tack 1o older, and still more generally used method, a to cohere readily and remains in an easily desheet of vulcanized calendered rubber is wrapped formable plastic state, but exhibits a substanin several layers upon a large drum, the drum is tial amount of resiliency, particularly in itsouter caused to rotate and the sheet is cut into threads or'face portions, and then progressively subjectby means of a rotary knife mounted upon a ing the sheet to pressure applied at opposed 15 lathe-like-moving support. In a more recently points along parallel lines upon the two faces'of devised method, liquid latex is extruded through the sheet to press opposite faces of the sheet a round nozzle into a coagulant and the ex-' along such lines into cohesive relationship and truded rubber filament is vulcanized to produce to deform the coagulum between such lines in a smooth surfaced round rubber thread Neither such manner as to place at least one of the faces method is entirely satisfactory. The thread of the intervening'portions of coagulum under produced. by the first described method has considerable tension, then severing the sheet square cut corners which sometimes are irregualong the lines of cohesive engagement of the two lar and tend to chafe easily when the thread is faces, to form a plurality of strips of coagulum,

subjected to certain types of service and is furwhich immediately upon severance of the sheet ther not well adapted for use in textile 'machinand consequent release of the restraining forces ery designed to weave round textile threads. assume a substantially rounded cross-sectional Although the advent of the smooth round exconfiguration by reason ofthe deformation of truded thread eliminated some of these disadthe plastic coagulum effected by forces tending to vantages of square cut thread, it has not proved equalize tension in the outer resilient portions of 3 to be satisfactory in all respects. Thus, it has the deformed coagulum. I accomplish this probeen found that the round extruded thread, cedure by forming from liquid latex a sheet of when provided with a textile wrapping and woven latex rubber coagulum, preferably containing together with textile threads to make an elastic fifty to seventy per cent. rubber (total solids) by fabric, will slip and fail to maintain its proper weight and thirty to fifty per cent. water, such position or relationship in the woven structure, as a sheet formedfrom the concentrated latex apparently because it is extremely smooth and of commerce without substantial loss of water, presents few surface irregularities and conse-. and then cutting the sheet, preferably after only quently little frictional resistance to prevent slipslight surface drying, into a plurality of strips,

page of the associated textile threads over its with a device capable of cutting with a true 0 surface. a a shearing action simultaneously along a plurality Accordingly, the objects of the present invenof parallel lines. I have found that a rotary tion include the manufacture of a rubber thread multiple disc shear in which the discs interlace possessing the weaving and processing advanslightly and have substantially right angular tages of round thread, which at the same time cutting edges is particularly well adapted to ac- 45 will not slip from its proper position when woven complish the deformation and severance of the into a fabric; the manufacture of a substantialplastic sheet to produce round strips. The manly round rubber thread having slight surface irner in which this device operates upon the sheet regularities adapted to increase frictional reof coagulum to accomplish this unexpected resistance of the thread without detracting from suit will be set out in detail hereafter. At this 5 its resistance to chafing; the provision of a novel point, it will suffice to say that in this manner method of making from liquid latex a substan- I produce a substantially round or cylindrical tially'round rubber thread; the provision of a rubber thread, the hemi-cylindrical surfaces of method for forminga sheet of latex rubber and which originally were portions of opposite faces for cutting the sheet to produce a rounded of the sheet of rubber coagulum, which faces, 55

in the thread, are effectually sealed or healed together by coherence of the rubber along approximately diametrically opposed longitudinal lines upon the thread surface. Along such lines of jointure are slight surface irregularities resulting from the formation of the sealed joint, which add materially to the frictional resistance of the thread and prevent its slippage when woven with textile thread, but apparently do not decrease chafing resistance as do the irregularities in prior square cut threads.

The invention will be more fully described with reference to the accompanying drawing, in which Fig. 1 is a diagrammatic elevation of apparatus adapted for carrying out the method of my invention.

Fig. 2 is a section taken on lines 2-2 of Fig. 1, illustrating more clearly the rotary multiple disc shear which is a part of the apparatus of Fig. 1.

Fig. 3 is a section taken on line 3-3 of Fig. 2.

Fig.4 is anenlarged partial section taken on line 4-4. of Fig. 3, showing only a few of the discshearsand illustrating their action upon a sheet o'f'rubber coagulum just as the discs come into cutting relationship.

Fig. 5is an enlarged partial section taken in the'axial plane of the discs on line 5-5 of Fig. 3.

. Figs. 6, 7 and 8,are sectioned perspective views of short lengths of rubber threads produced by the present invention.

The preferred apparatus illustrated in the drawing comprises a hollow sheet metal deposition drum ll) rotatably mounted and provided with water pipe connections II for circulating cooling water through the interior of the drum. The-drum is rotated by means of a sprocket l2 and chain i3 deriving power from a source not shown. The lower portion of the drum dips into a body of latex l4 contained in a rectangular sheet metal tank l5 which is provided with a water jacket l6 through which cooling water may be circulated by means of pipe connections H and i8. Porous diaphragms I9 made of unglazed porcelain, asbestos, or similar material are inserted in the deposition tank near the surface of the deposition drum and serve to separate the latex from the cathode liquid 20 which may be ordinary tap water, or a solution of a neutral conductive salt such as ammonium chloride or ammonium nitrate, surrounding metallic cathodes 2l which are-inserted in both ends of the tank-and are connected to the negative terminal of a source of directcurrent (not shown). The positive terminal of the source of current is connected to a brush 22 which contacts with a slip ring 23 mounted on the drum shaft through which current may be conducted to the drum itself. The sides of the deposition drum are coated with an insulating paint or varnish, or with a thin layer of rubber to insulate them from the latex, and the peripherial surface 24 of the drum preferably is made of zinc, cadmium, or similar metal capable of anodic solution without generation of gas. A stripping roller 25 of small diameter is rotatably mounted with its surface almost in tangential contact with the surface 24 of the deposition drum l0 so that it may effectively strip a sheet of deposited rubber from thedrum and deliver it to a conventional belt conveyor 26 arranged to convey the sheet to a mul-,

tiple disc rotary shear 30.

The rotary shear comprises a bed plate 3|, and two vertically slotted side frame members 32 connected at their upperextremities by tiebars or plates 33. In the vertical slots in each of the -'40, which are separated by spacing rings or discs 4| of smaller diameter but of the same width as the shear discs 40, that width being substantially equal to the diameter of the thread or width of the strip to be made plus allowance for shrinkage of therubber which occurs on drying. The shear discs 40 are of such diameter that, when they are mounted upon the arbors in the manner described, the disc peripheries will overlap or interlace slightly, to provide a true disc type shear. The shear discs 40, and spacing discs 4| are held in place by pressing them against shoulders 42 at one end of each arbor by tightening threaded collars 43 at the opposite ends of the arbors. Two series of metal fingers 44 somewhat narrower than the shear discs are clamped upon supporting bars 45 so that the fingers extend into the spaces between the several shear discs at a position well past the cutting region of the shears, the function of these fingers being to aid in removing cut strips from the spaces between the shear discs,

Beyond the shearing apparatus is provided a pair of conventional endless belt conveyors 46 arranged one above the other in position to receive cut strips of rubber coagulum from the shearing device and to convey them horizontally through a tunnel dryer 41 heated as by hot air circulated through the dryer by means of ducts 48. If desired the dryer may be made sufiiciently long, and heated to a temperature adequate to vulcanize as well as to dry the coagulum. Under the delivery ends of the conveyors are provided boxes 49 into which the threads may fall preliminary to being wound or reeled upon bobbins 50.

When the apparatus is in operation, direct current flows through the brush 22 to the body of the deposition drum l0, through the zinc surface 24 to the body of latex l4, thence through the porous diaphragms, which are saturated with electro-conductive fluid, into the cathode liquid 20 and thence out through the cathodes 2|. Under the influence of the current, the negatively charged particles of rubber and otherv solids suspended in the latex migrate toward and are deposited upon the peripherial surface of the rotating deposition drum to form a continuous sheet 5| of water-containing latex rubber coagulum, preferably of a thickness approximately equal to the width of the disc shears, which sheet is continuously stripped from the drum after it emerges from the body of the latex by means of the stripping roller 25, and is carried by the conveyor 26 to the multiple disc rotary shear 30.

The sheet of coagulum preferably is not heated or otherwise dried except for the slight natural surface drying which results from exposure to the atmosphere during the period after its emergence from the latex, but slight artificial drying during this period is not prohibited and in some cases may be desirable, particularly when conditions of operations are such that surface portions of the sheet are not sufficiently resilient to produce the desired effect upon shearing the rubber. The drying of the sheet however should not be carried further than is necessary to secure the opposite faces of the sheet, are in feifect the requisite surfaceresiliency and should never go. so far as substantially to [dry the sheet,

throughout its body. Ifjslightlfforcedflsurface dryingis'idesired, asuitable heating chamber,

may be provided about the conveyor 26.

The plastic and deformable but somewhat re silient and quite cohesiyeshe'et of waterfcontain ing coagulum then is dilct d into thefbight or the disc shears and as it" progresses toward the pinched more and more closely together along the parallel lines 'determined by the several in? terl'acing upperandlowefldiscs. This pinching operation necessarily stretches the freefacesff 'of the as yetjunseveredj intervening strips'of'co-r,

agulum and sets up substantiaHytensional forces in the surface portions thereof which, in, obey ance to well known physical laws, assume a rounded, :practically semi-circular cross-section al configuration. These surface tensional forces are maintained and increased by the progres-' sively pinching shears which press the opposite v faces of the sheet closer and closertogether with consequent, progressively increased stretching of the free "facesfof the coagulum until finally when the sheet reaches, the cutting region of the shears and is severed along'lines containing the points. 0, opposite faces of thesheet are, by the shearing action, brought into actual contact u (her high pressure and are pinched together. As a a result oflthis pinching and of the cohesive character of the coagulum, the formerly opposed faces of the sheet cohere along their Q severed edges so] that upon release of the tensioning forces, which accompanies severance of the sheet, the free faces of the now severed strips contact .circumferentially under the internal tension, thereby circumferentially stretching the formerly vunfree faces u of the strips and setting; up tensional jforces therein until the tension and other forces throughout the stripfare equalized. This equalization of the internal 'forces of the strip further deforms the still plastic coagulum and causes 'it'to assume a substantially circular cross-sectional configuration as illustrated in Fig. 6. The equalization of internal forces and consequent shaping of the strip occurs immediately upon severance of the strip even though it is closely confined between the faces of the discs, because sufficient water-an excellent lubricant for rubber-4s expressed from the coagulum by the shearing operation to lubricate its surface thoroughly and to allow its easy movement along the sides of the shear discs. The several cut strips 52 of coagulum are separated by the shearing operation into upper and lower sets of alternating strips, which are directed respectively to the upper and lower conveyors to be dried and vulcanized in any suitable manner to produce finished rubber threads of substantially circular cross section, each of which exhibits two substantially diametrically opposed longitudinal seams 53 along the lines of cohesion of the opposite faces. The seams in most cases occur as continuous or discontinuous slightly projecting pressions 154 along the threads'as inlF'igl "7,

although the effective crosssec'ti'on o'fthe thread remains substantially circular.

it is ,by no means limited to such manufacture, and may be employed with. equally satisfactory resultsjfor making strips or i example, if a sheet of coagulum is ,cut with, a

rotary disc, shear in which'the discs'are'com. thickness oft'he sheet} siderably wider, than the i a generally flat. strip 55 having rounded edges of substantiallycircular conflguratlonwill be pro- Diametrically, opposed. longitudinal duced, seams '56, are evident along theapp'roximat e center ofthe rounded, edgesof such flat strips, just as in the round threads. It is-apparent that the open fslightly fto produce cohcail'e de-l bands of rubber. For.

strips having oval, oblate spheroidal, and other.

rounded cross-sectional configurations may {be produced b'y'varying, the widthof thediscs with relation to the thickness of the sheet of coagulum The many advantages 'o'f the present method andits' product are manifest. It provides for the manufacture of a efiicient, rapid, and economical rubber thread which is particularly adapted'for combining with textile threads or woven fabrics, but offcourse may be used in many otherapplicas tions just as former types of elastic thread are; used, It produces rounded'threads such as are] required for weaving, and at the same time pro-v vides suificieht surface irregularities in the thread to impart to it frictional resistance; adequate to prevent its slippage in a woven structure. The) method iscapable of continuous operation and is exceedingly well adapted for commercial produce.

tion in that the apparatus required is compact,

simple and relatively inexpensive.

scribed procedure and apparatus. Thus, the sheetof rubber coagulummay be formed by coating'a. moving surface with a latex coagulant and V .40 It is obvious'that many modifications and vial riatio'ris are possible in' details or the above der."

immersing the coagulant-coated surface into latex to deposit a sheet of rubber upon thesur-V facef'or a porous surface may be immersed in the latex to acquire arubber deposit, or latex may be spread allowed in sheet form on to a moving.

surface, or other methods'of forming a latex' sheet possessing the requisite properties of re-Q,

siliency,deformability and cohesiveness "may be employed. Equivalent apparatus including other types of shears may be substituted for that shown without departing from the scope of the invention.

Although I have illustrated the'rubber thread produced by my invention as having an effective cross-section which is substantially circular, or in the case of flat bands, as having a circular edge, it is to be understood that in practice, the actual cross-sections of the threads may vary somewhat from perfect geometric proportions and that the seams may not in all cases be exactly in diametric opposition. Accordingly, when I use geometric terms in the specification and claims in describing the thread of this invention, it is to be understood that such terms are intended to include all such variations in proportions and are not intended necessarily to refer to exact geometrical configurations.

The term latex has been used in a generic sense to include all natural and artificial aqueous dispersions of rubber, gutta-percha, balata, and similar natural or synthetic gums, whether in the unvulcanized, vulcanized, or reclaimed condition. The latex may be thickened, thinned, concentrated, diluted, vulcanized or otherwise preliminarily treated and may contain any desirable thickening, thinning, stabilizing, or other conditioning agents. Compounding ingredients such as vulcanizing agents, accelerators, age-resistors, fillers, pigments, softeners, etc. may be admixed with the latex as desired.

I claim:

1. A vulcanized rubber thread comprising an elongated strip of unmasticated latex rubber having the native colloidal structure of rubber deposited directly from liquid rubber latex, said strip having two opposed uncut faces and two opposed cutfaces, the opposed cut faces exhibiting the characteristics of rubber faces cut by a shearing operation.

2. A vulcanized latex rubber thread having a cut edge and a line of surface irregularity extending longitudinally of the thread along the approximate mid-portion of the cut edge, said surface irregularity comprising a longitudinally extending reentrant groove serving to increase frictional resistance of the thread surface.

3. A vulcanized rubber strip having a cut edge and a seam extending longitudinally of the strip along the approximate mid-portion of the cut edge.

4. The method which comprises forming directly from liquid rubber latex a coherent sheet of latex rubber coagulum containing a substantial percentage of water distributed through the coagulum, progressively applying pressure to opposite faces of the sheet along a plurality of substantially opposed parallel lines upon the two faces of the sheet, and within the region of applied pressure simultaneously with the application of the pressure confining one face of each of the strips defined by said lines while leaving the opposite face of eachof said strips unconfined, the adjoining faces of contiguous strips being alternately confined and unconfined, and severing the sheet along said lines.

5. The method which comprises forming directly from liquid rubber latex a coherent sheet of latex rubber coagulum containing a substantial percentage of water distributed through the coagulum, subjecting a plurality of parallel spaced zones of the sheet .to progressive pressure applied from one side of the sheet substantially normally to the plane thereof and simultaneously subjecting the intervening zones to a like pressure applied from the other side of the sheet whereby adjacent parallel zones are urged in opposite directions out of the normal plane of the sheet and the sheet is severed along the margins of said zones to produce strips of coagulum.

6. The method which comprises forming directly from liquid rubber latex a microporous sheet of cohesive and easily deformable but somewhat resilient rubber coagulum containing a substantial percentage of water distributed throughout its microporous structure, applying pressure to opposite faces of the sheet along a plurality of substantially opposed parallel lines upon the two faces of'the sheet to press opposite faces of the sheet along said lines into cohesive relationship and to deform the coagulum between said lines in such manner as to place at least one of the faces of the intervening portions of coagulum under tension, and severing the sheet along the lines of cohesive engagement of the two faces, to produce strips of coagulum having substantially rounded severed edges, and drying the strips of coagulum.

7. The method which comprises forming directly from liquid rubber latex a microporous sheet of cohesive and easily deformable but somewhat resilient rubber coagulum containing a substantial percentage of water distributed throughout its microporous structure, and shearing the sheet of coagulum along a plurality of parallel lines to produce strips of rubber coagulum having substantially rounded edges, and drying the strips of coagulum.

8. The method which comprises forming directly from liquid rubber latex a sheet of watercontaining rubber coagulum and drying the sheet to the extent only that the coagulum retains sufficient surface tack to cohere readily and remains in an easily deformable state, but exhibits a'substantial amount of resiliency in its surface portions, and progressively shearing the sheet of coagulum along parallel lines to produce strips of rubber coagulum having substantially rounded edges, and drying the strips of coagulum.

9. The method which comprises eleotro-depositing rubber from liquid rubber latex upon a moving surface to form continuously a coherent sheet of water-containing coagulum, and while the sheet still contains a substantial part of the water which was deposited with the rubber from the latex, progressively shearing it simultaneously along a plurality of parallel lines of shear and drying the sheared strips to produce a plurality of rubber strips having rounded edges.

CARL L. BEAL. 

